Brush seals are commonly used to eliminate or reduce air leakage through a gap between adjacent parts or components. For example, brush seals may be positioned about rotating components within turbine engines used for power generation and the like. Typically, the brush seals reduce the leakage between regions at different air pressures. As a specific example, a brush seal may be used to reduce air leakage through the gap (or the clearance) between a stationary component such as a stator and a rotating component such as a rotor. A brush seal may be a contact seal with a number of bristles in contact with the rotor surface. The bristles allow for a tight clearance with reduced leakage as compared to most non-contact seals such as labyrinth seals and the like.
Brush seals, however, may undergo substantial wear due to the interference between the bristles and the rotor caused by transient events during, for example, turbine startup or shutdown. During these transient events, the rotary machine may experience considerable temperature gradients, differential growth, vibrations, and other types of dynamic behavior. This wear may accumulate over a number of startup/shutdown cycles so as to reduce the leakage performance of the seal during steady state operations. Wear on the bristles generally correlates with an overall decrease in turbine efficiency and power output.
One response to such transient events has been the use of radially retractable brush seals such as variable clearance positive pressure packing (“VCPPP”) seal technology and the like. Generally described, VCPPP seal technology radially retracts the brush seals during startup so as to limit wear. Such radial movement, however, generally requires large segment gaps to accommodate the radius change. These segment gaps can drive additional leakage. The brush seal ring also may have the risk of failing to close properly if contaminants and the like accumulate therein. For example, bristles at the segment ends may fall into the gap when the brush seal ring opens up.
There is thus a desire for an improved retractable seal system that eliminates or reduces the impact of transient events and the like. Such an improved system should provide overall seal system predictability, reliability, and an increased life time with reasonable costs.